The present disclosure relates to a separator and a non-aqueous electrolyte battery and, more particularly, to a microporous separator and a non-aqueous electrolyte battery having a cathode, an anode, a non-aqueous electrolyte, and the separator.
Owing to the remarkable development of a recent portable electronic apparatus technique, cellular phones and notebook-sized computers are appreciated as a basic technique which supports an advanced information society. Studies and development regarding a technique for realizing advanced functions of those apparatuses are vigorously being progressed. There is such a problem that a driving time is reduced by an increase in electric power consumption due to the advanced functions.
To assure the driving time of a predetermined level or longer, it is indispensable to realize a high energy density of a secondary battery which is used as a driving power source. Therefore, in a secondary battery having an advanced function represented by, for example, a lithium ion secondary battery or the like, it is expected to accomplish the higher energy density.
In the lithium ion secondary battery in the related art, lithium cobalt acid is used for a cathode, a carbon material is used for an anode, and an operating voltage is set to a value within a range from 2.5 to 4.2 V. In a single battery, a terminal voltage can be raised to 4.2V owing to an excellent electrochemical stability of a non-aqueous electrolyte material, the separator, and the like.
On the other hand, a cathode active material such as lithium cobalt acid or the like which is used in the lithium ion secondary battery in the related art which operates at the maximum voltage of 4.2V merely uses a capacitance of about 60% of its theoretical capacitance and a residual capacitance can be utilized in principle by further raising a charge voltage. As disclosed in International Publication No. WO03/019713A1, the high energy density can be realized by setting the voltage upon charging to 4.25V or more.
However, a polyolefin microporous membrane used in the non-aqueous electrolyte secondary battery has the following problem. If the charge voltage is set to 4.25V or more, particularly, an oxidation atmosphere near the cathode surface is enhanced, so that the non-aqueous electrolyte material and the separator which physically come into contact with the cathode are easily subjected to oxidation decomposition. Thus, an internal resistance increases and battery characteristics deteriorate. Even if the charge voltage is smaller than 4.25V, it is preferable to suppress the deterioration of the battery characteristics by using the separator having an oxidation resistance.
It is, therefore, desirable to provide a separator and a non-aqueous electrolyte battery which can suppress a deterioration of battery characteristics.